The beautiful New York Times confirms something everybody notices: spam is doing very well. "In the last six months, the problem has gotten measurably worse. Worldwide spam volumes have doubled from last year, according to Ironport, a spam filtering firm, and unsolicited junk mail now accounts for more than 9 of every 10 e-mail messages sent over the Internet."
The techniques responsible for this growth are image spam and the use of "vast networks of computers belonging to users who unknowingly downloaded viruses and other rogue programs".
Spammers try to fool message filters by using excerpts from books or articles. OCR software is not very effective because image spams use special effects, background images and weird fonts.
Traditional spam is still effective, as many mail services don't have powerful spam filters.